1. Field of the Invention
The invention relates generally to the field of communications systems and specifically to diagnosing error conditions in high-speed communication systems.
2. Description of the Related Art
In many communications systems there is a need to troubleshoot the network's to make sure that the network cabling has been installed according to specification and is operating properly. Thus, network testing and diagnostics are extremely useful to monitor the network and warn the network manager of impending problems. Furthermore, network testing and diagnostic testing systems may be designed to gather useful information about the conditions of a network and provide statistical information about the equipment connected to the network. For instance, the diagnostic testing system may be programmed to identify the conditions of coupled external systems. In a high-speed communication system, for example, characteristics of the communications channel such as the length of the link, noise, and signal attenuation and distortion through the channel may be important factors affecting the quality of the system. Noise testing is important because such testing aids in the detection of crosstalk. Crosstalk is noise emanating from the signals transmitted on adjacent wire pairs. Namely, the crosstalk is the generation of undesired signals from another circuit in the same system.
There may be cases where channel impairments are so drastic that it is not even possible to establish a communication link between or within systems. Having the ability to quickly identify the conditions resulting from a failure and the possible causes of the channel impairments may permit the user of the communication system to take remedial action thus minimizing the costs attributed to the failure. Identifying and solving the problems that has led to the failure would be greatly facilitated if the communication system itself was designed with enough intelligence to self-diagnose the cause of the failure and report the cause to the user. However, most conventional diagnostic devices are tools that technicians carry around with them to troubleshoot the network's problems.
A Gigabit Ethernet in copper-based Local Area Networks (LANs) is an exemplary communications system that may benefit from such a self-diagnosing diagnostic measurement device. Other popular communication systems, which may benefit from such diagnostic testing devices, are known as the 100Base-TX Fast Ethernet standard and 10Base-T standard which are adaptations of the IEEE (Institute of Electrical and Electronic Engineers) 802.3 standard. The 10Base-T standard relates to twisted-pair cables having a maximum segment lengths of 100 meters. The 100Base-TX standard, which is based on the transmission over Category-5 Unshielded Twisted Pairs (UTP-5), has found widespread application in recent years. However, the need for higher data rates has prompted the development of an even higher speed transmission standard, the IEEE 802.3ab, also known as 1000Base-T. Communication systems based on the 1000Base-T standard transmit at 1 Gb/s, also using Category-5 UTP.
However, there are important differences in the manner in which the Category-5 cable is used in 100Base-TX versus the 1000Base-T. For example, 100Base-TX is essentially a half-duplex transmission scheme, where full-duplex operation is achieved by using one pair of the UTP-5 cable to transmit signals and another pair to receive signals. The UTP-5 cable has four-twisted pairs, therefore two of the pair of twisted wires typically remain unused in 100Base-TX. On the other hand, 1000Base-T provides full-duplex transmission over the four pairs of the UTP-5 cable. This means that each pair of wire is used both to transmit and receive the signals. The transmitted and received signals, which coexist in the cable, are separated at the receiver using echo cancellation techniques. To achieve an aggregate data rate of 1 Gb/s, the four pairs of the UTP-5 cable are used, each one supporting a data rate of 250 Mb/s. Since 1000Base-T uses the same cabling as 100Base-TX, the transition to the higher speed standard 1000Base-T can be made using the same cabling system without the need to rewire a building or install new cable. However, since 100Base-TX does not use two of the four pairs of the UTP-5 cable, it is possible that in many installations the two unused pairs may be improperly connected. Since these two pairs may have been unused, any faulty connections may have gone undetected. These faulty connections would have to be identified and fixed in order for the 1000Base-T system to work using the 100Base-TX cabling system. Such diagnosis could add to the cost of installing 1000Base-T to a system, even if no rewiring is needed in principle.